"You may be the best technical scrummager in a game, but you will not be effective if are not able to perform after the first few minutes due to fatigue. Research undertaken in 1992 (McLean, 1992, Journal of sports sciences) indicated that there were between 24 and 45 scrums in a 5-Nations match, so endurance is essential (and the game physical demands of the game have advanced since this research, due to professionalism and law changes making the game quicker!).
Similarly, a scrum-half who cannot be at every breakdown to begin the next phase of play after every ruck and maul will never reach the top, and if he is not powerful or fast enough to exploit space around the base of the scrum, his game will lack a dimension.
Above are two examples highlighting examples of some positional demands of the players. However, every player (regardless of his position) needs to be able to work at high intensities with small rest breaks for 80 minutes. Top level players will run between 4000m and 6000m in a game (bearing in mind that 5000m constitutes an endurance event in athletics), much of it at high intensities."
Strength endurance...cardio endurance...strength endurance...cardio endurance...strength endurance......cardio endurance...make it your mantra.
I'd put the endurance and physical conditioning of top flight ruggers against just about anyone.